(a) Field of the Invention
The present invention relates to an ion concentration measuring method and apparatus for electrically measuring a concentration of ions present in a liquid solution.
(b) Description of the Related Art
An ion concentration measuring apparatus measures a membrane potential generated in an ion sensing layer in contact with a solution and displays the measured membrane potential, and recently, application of the ion concentration measuring apparatus has extended to biosensors and gas sensors. For example, a typical ion concentration measuring apparatus detects hydrogen ions and displays a degree of pH.
The ion concentration measuring apparatus may detect an ion concentration using a semiconductor transistor according to a semiconductor detection method. In the related art semiconductor detection method, an ion sensitive field effect transistor (ISFET) is used. The ISFET refers to an FET in which an ion sensing layer replacing a metal electrode is provided at a gate part of a metal oxide semiconductor field effect transistor (MOSFET), in order to have ion selectivity. Using FET characteristics reacting to a potential on the ion sensing layer (that is, an interface potential), an ion concentration may be measured by indirectly measuring the interface potential. The semiconductor detection method is advantageous in that a response time is fast, allows the ion concentration detection apparatus to become compact and integrated, and allows for mass production.
In the related art ion concentration measuring apparatus using the ISFET, a single transistor including an ion sensing layer is used and an interface potential is induced as a voltage or a current at a source or a drain region of the ISFET, whereby the interface potential is indirectly measured. In the related art method, however, loss occurs in the process of inducing the interface potential as a voltage or a current at a source or a drain region, making it difficult to measure a fine interface potential (a potential on the ion sensing layer). Also, in the related art, since the single transistor including the single ion sensing layer is used, a measurement magnitude with respect to a membrane potential is limited to single transistor characteristics. With the method for measuring an ion concentration using a semiconductor, shielding (passivation) a solution such that it does not affect operation of a transistor or a circuit unit is important. However, in the related art ISFET, since the ion sensing layer and the transistor are positioned to be close up and down, a shielding process is difficult to perform and stability is degraded.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.